A Rapid Evaluation Method for Creep Properties of Directionally Solidified Nickel-Based Alloy DZ411

Effects of pre-strains (0.5%, 1.0%, 1.5%, 2.0%, 2.5%), loading strain rates (4.0×10^-5, 1.2×10^-4, 4.0×10^-4 s^-1) and initial temperatures (750, 900 ℃) of continuous temperature stress relaxation tests on directionally solidified nickel-based alloy DZ411 were studied. Based on steady-state deformation obtained by dynamic equilibrium of work hardening and recovery softening, assuming that the change of the steady-state relaxation strain rate with stress was consistent with that of the minimum creep rate of the traditional creep rupture test, the minimum creep rate was predicted and verified by short-term stress relaxation tests. The results show that the test alloy was relaxed when the work hardening and recovery softening were in dynamic equilibrium. When the pre-strain was not less than 1.0%, the steady-state relaxation could be quickly achieved. The initial temperature had little effect on the steady-state relaxation behavior. The loading strain rate affected the initial relaxation strain rate, but had little effect on the change of steady-state relaxation strain rate with stress. The minimum creep rates under different temperatures and stresses could be predicted by the master curve of steady-state relaxation strain rate. The creep rupture test results were located in the range of 99% reliable curve of the master curve of steady-state relaxation strain rate.